Quantifying nitrous oxide fluxes on multiple spatial scales in the Upper Midwest, USA

Area of Science:

• Agricultural Science
• Environmental Science
• Atmospheric Chemistry

Background:

• Nitrous oxide (N2O) is a potent greenhouse gas with significant agricultural contributions.
• Understanding N2O budgets in major cropping systems is crucial for climate change mitigation.

Purpose of the Study:

• To quantify the contribution of soybean and corn plants and their associated ecosystems to the regional N2O budget in the Upper Midwest, USA.
• To differentiate N2O fluxes at plant, soil-plant ecosystem, and regional scales.

Main Methods:

• Utilized novel steady-state flow-through plant chambers for plant-scale flux measurements.
• Employed a flux-gradient micrometeorological tower for ecosystem-scale flux quantification.
• Leveraged continuous tall-tower observatories for regional N2O budget analysis.

Main Results:

• N2O fluxes from soybean and corn plants were significantly lower (by an order of magnitude) than those from the soil-plant ecosystem.
• Fertilization temporarily increased corn N2O flux and significantly elevated soybean N2O emissions late in the season.
• Direct N2O emissions from cropland constituted less than 20% of the regional flux, indicating substantial contributions from other sources and indirect pathways.

Conclusions:

• Cropland N2O emissions are predominantly soil-driven, with plant contributions being minor.
• Fertilization strategies and timing critically influence N2O emissions from agricultural soils.
• Regional N2O budgets are complex, influenced by direct emissions, indirect emissions, and potentially non-cropland sources.